The present invention relates to a piezoelectric vibrator capable of vibrating in an expansion mode of vibration and, more particularly, to the vibrator comprising a piezoelectric vibrating element composed of a vibrateable substrate, made of a constant elastic metal, i.e., a metallic material having a constant modulus of elasticity, a thin film of piezoelectric material and an exciting electrode layer.
In the piezoelectric vibrator of the type referred to above, it is generally well known that some vibrating characteristics of the vibrator such as, for example, the capacity ratio .gamma.(=C.sub.D /C.sub.O) and the difference .DELTA.F between the resonance and anti-resonance frequencies can be improved if the thickness of the vibrateable substrate is small. However, the reduced thickness of the vibrateable substrate often constitutes a cause of reduction in physical strength and/or of warp which would occur in the vibrateable substrate during the formation of the piezoelectric thin film thereon by the use of a sputtering technique. Therefore, the extent to which the vibrateable substrate can be reduced in thickness has been limited.
In view of the limitation imposed on the capability of reducing the thickness of the vibrateable substrate, countermeasures have hitherto been employed in such a way as to render the vibrateable substrate to have, instead of the square shape, a generally rectangular shape as shown in FIG. 5(a), a shape generally similar to a tie bow as shown in FIG. 5(b), or a shape generally similar to a butterfly as shown in FIG. 5(c), or any other shape modified from the shape shown in any one of FIGS. 5(a) to 5(c).
However, it has been found that, even though the shape of the vibrateable substrate is carefully designed and chosen, the vibrating characteristics cannot be improved so much as expected, and therefore, demand has been made to provide an effective resort to achieve it.